This application claims the benefit of co-pending German Patent Application No. 199 28 113.0 entitled xe2x80x9cAnhxc3xa4ngerbremsventil far blockiergeschxc3xctzte Druckluftbremsanlagen von Anhxc3xa4ngernxe2x80x9d filed on Jun. 19, 1999.
The present invention generally relates to a brake valve. More particularly, the present invention relates to a trailer brake valve to be used in a compressed air brake system of a trailer of a truck. The brake system or the brake assembly of the trailer includes an anti lock control unit (ABS control unit) and a load sensing control unit (ALB control unit). The trailer brake valve is a control valve being designed as a relay valve and being arranged at the trailer of the truck. The trailer brake valve serves to control brake pressure in the region of the brake of the trailer of the truck. The trailer itself also includes an anti lock system. Additionally, the trailer includes at least one sensor indicating the load of the trailer and providing a corresponding signal. In case the trailer includes a suspension or a pneumatic cushioning, the sensor may simply sense the pressure in a filling conduit being connected to a suspension bellow.
A trailer brake valve is known from German patent No. 35 19 182 C2. The trailer brake valve includes a relay piston being guided in a housing. The relay piston defines a control chamber and a brake chamber in the housing. The brake conduit of the trailer is connected to the control chamber. The brake chamber includes connections for conduits leading to brake cylinders.
The known trailer brake valve includes an inlet valve and an outlet valve including a common double valve body. The inlet valve is located adjacent a reservoir chamber being permanently connected to a reservoir conduit leading to the trailer and to a reservoir at the trailer.
The known trailer brake valve includes an anti lock electronic control unit being integrated into the housing of the trailer brake valve. A pressure/voltage converter detects the control pressure prevailing in the brake conduit, and it is electrically connected to the anti lock electronic control unit to transmit the signal. The known trailer brake valve includes a solenoid valve. The solenoid valve is arranged in the brake conduit leading to the control chamber of the relay piston, and it has a special design.
The known solenoid valve has three possible positions. In the non-excited position of the known solenoid valve, there is a passage in the brake conduit in the direction of the control chamber of the relay piston. In a first excited position of the known solenoid valve, this passage is blocked and a conduit leading to an expansion space is also blocked. In a second excited position of the known solenoid valve, the brake conduit is blocked and the side of the entrance, again, but the connection to the expansion space is freed such that the pressure prevailing in the control chamber is correspondingly reduced. The expansion chamber may be connected to the atmosphere by a throttling bore.
The known trailer brake valve includes a steering mechanism for a load signal. This means that it includes the connection of a mechanical adjustment drive, the position signal of which is fed into the anti lock electronic control device such that the solenoid valve and its inlet, respectively, is closed in steps corresponding to the present load of the trailer. Due to the connection of the control chamber to the expansion space, it is possible to reduce the pressure by one corresponding step. The value of this step depends on the volume of the expansion space.
In many cases, it is not sufficient to reduce the control pressure by one step by a connection of the control chamber to the expansion space. The connection of the expansion space to the atmosphere via a throttling bore has the effect of the pressure being reduced in the expansion space. Nevertheless, the pressure often is not reduced fast enough to remain under the locking limit in the anti lock operating modus.
With the known trailer brake valve, the effect of the load signal (ALB signal) is lost when the power supply of the anti lock electronic control unit (ABS electronic control unit) fails. Thus, the trailer only brakes pneumatically. There is the danger of the trailer braking too much and of the wheels of the trailer locking, respectively.
A brake assembly for pneumatically braking trailers is known from German patent application No. DE 44 25 789 A1. The brake assembly includes an electronic control unit for an anti lock control not only processing anti lock signals (ABS signals), but also additionally processing load signals (ALB signals). When the power supply of the known electronic control unit fails or in case of a different defect occurring in the electronic control unit, the anti lock signal and the load signal do not have an effect any more. In case of such a defect occurring and a brake signal being sent to the trailer by the trailer control valve being located at the truck, the trailer brake pressure is no longer adapted to the driving conditions.
It is also known to use two solenoid valves with prior art relay valves being operated together with an anti lock electronic control unit. The solenoid valves are either located on the truck or on the trailer. The first solenoid valve serves to aerate the control chamber of the relay valve, and the second solenoid valve serves to deaerate the control chamber of the relay valve.
Typically, it is known in the art to use two solenoid valves at one relay valve when an anti lock signal is processed and when the pressure prevailing in the control chamber of the relay valve is to be increased, decreased or kept constant for a limited period of time.
Briefly described, the present invention provides a trailer brake valve. The trailer brake valve is to be mounted in a compressed air brake system of a trailer of a truck. The brake system of the trailer includes an anti lock control unit and a load sensing control unit. The trailer brake valve includes a housing and a relay piston being movably guided in the housing. A control chamber is located in the housing. A brake chamber is located in the housing, and it includes connections for conduits leading to brake cylinders of the brake system in which the trailer brake valve is to be mounted. The control chamber and the brake chamber are defined and limited by the relay piston. A brake conduit is connected to the control chamber. A reservoir chamber is located in the housing and an inlet valve is located adjacent the reservoir chamber. An outlet valve is located in the housing. A first solenoid valve is arranged in the brake conduit and a second solenoid valve is designed and arranged to deaerate the control chamber. A first pressure/voltage converter is designed and arranged to sense control pressure prevailing in the brake conduit and a second pressure/voltage converter is designed and arranged to sense pressure prevailing in a region adjacent the relay piston. A load sensing control unit is designed and arranged to produce a load signal and an independent electronic control unit is designed and arranged to control the first and second solenoid valve exclusively with the load signal produced by the load sensing control unit.
The present invention is based on the concept to separate the processing of the anti lock signal (ABS signal) from the processing of the load signal (ALN signal) in a compressed air brake assembly of a trailer including an anti lock control unit and a load sensing control unit, and to provide the trailer brake valve with its own electronic control being designed and destined to exclusively process load signals. The trailer brake valve includes two solenoid valves of which the first serves to aerate the control chamber and of which the second serves to deaerate the control chamber. Consequently, a great variety of possible control philosophies are realized for the trailer brake valve.
With the novel brake valve of a trailer of a truck (a xe2x80x9ctrailer brake valvexe2x80x9d), it is possible to safely control the brake pressure of the trailer at least with respect to the value of the load of the trailer (how much mass and weight, respectively, is loaded on the trailer) in case power supply of an anti lock system failing or a in case of a different failure.
The braking processes may be adjusted with respect to the locking conditions. The pressure in front of or behind the relay piston, meaning the pressure in the control chamber or in the brake chamber, is watched and monitored, and it is processed as an influencing variable in the electronic control unit. The trailer brake valve includes its own independent electronic control unit. The anti lock system includes an anti lock electronic control unit.
When such a novel trailer brake valve is used in combination with an anti lock system at a trailer, there is the special advantage of the load sensing function being maintained even when the electric power supply of the anti lock system fails or when a different failure occurs. This means that the load signal never loses its influence on the controlled brake pressure at the trailer brake valve.
There are a number of different possibilities of processing the load signal. The load sensing control unit may include a pressure/voltage transmitter being pneumatically connected to a suspension bellow and being electrically connected to the electronic control unit of the trailer brake valve. In this case, the trailer needs to be supplied with a suspension system or a similar apparatus.
It is sufficient if the first solenoid valve includes two positions, the passage in the brake conduit towards the relay piston being free in the first position and being locked in the second position. Preferably, the second solenoid valve includes its own deaerating opening and two positions, the deaerating opening being locked in the first position and being free in the second position. These two solenoid valves allow for control curves of various designs with corresponding special advantages.
Additionally, it is possible that the electronic control unit of the trailer brake valve includes a connection for an electric line leading to a control valve of a lifting axle. Thus, the lifting axle of the trailer is also controllable by the trailer brake valve. The load signal is directly used for this control. The control valve being located in the electric line may be designed as a 5/2-way valve by which the suspension bellows of the lifting axle and the lifting bellow of the lifting axle are controllable. The 5/2-way valve includes a connection for a compressed air supply, its own deaerating opening and a connection for a pneumatic connecting conduit being connected to the suspension bellows of the other axles.
The electronic control unit of the trailer brake valve may be designed to be freely programmable. In this way, for example, there is the possibility of processing the load signal during normal operating conditions. When the load signal fails, the operating condition may be changed to an emergency condition, for example to a partial load.
There also is the possibility of the trailer brake valve controlling a warning light to indicate a failure of the electronic control unit of the trailer brake valve or different undesired conditions. The warning light is arranged in a way that the driver is capable of visualizing the signal. For example, a different undesired condition is to be understood as a condition in which the trailer is overloaded.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and the detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention, as defined by the claims.